The cheapest way to fertilize your organic garden is to make compost in the backyard by recycling food scraps and yard waste. Bacteria, microbes, grubs and earthworms consume the organic waste. Worm castings are rich in nutrients that help plants grow. It also makes an attractive topsoil.
Dig a hole 2 to 3 feet deep by 2 to 3 feet wide. Line the bottom with corrugated cardboard. If you don't have corrugated cardboard, use shredded paper or newspaper. Use your garden hose to spray whatever paper product you use, so that it's wet but not soggy.
Dump your food scraps and yard waste in once or twice a week. Cover them with a layer of garden soil and more corrugated cardboard, so that you're layering paper products with green waste and then garden soil.
Spray the top layer of soil with water and cover it with a tarp. Leave it alone until it's time to add more green waste. Keep a small receptacle in your kitchen for things to compost, and dump it in weekly, using the same layering technique.
Continue the process of layering waste until the hole is filled. It's OK to make a heap by layering higher and higher. Compost can be made in as little as three months. Depending upon how much waste you're producing, start a new pile every few months to give your first pile time to mature.
Keep the pile covered with a tarp for up to three months. You can add worms to speed the process, but it is not necessary to do so. The microbes and bacteria will make compost, and worms from the yard will naturally be attracted to the compost.
Sift your compost through a wire mesh screen to separate the rich black soil from the things which haven't composted yet. Watermelon rinds, avocado peels, banana peels and other large items may take longer to compost. Pass these down into your next compost pile.
Sprinkle the compost over your flowerbeds to make a pretty, nutrient-rich, self-fertilizing topsoil. Work it into your raised vegetable garden soil or use it as potting soil.